Coordinating Tectons: Bipyridyl-Terminated Group ... - ACS Publications

Mar 19, 2009 - George A. Koutsantonis,* Gareth I. Jenkins, Phil A. Schauer, Barbara Szczepaniak,. Brian W. Skelton, Colin Tan, and Allan H. White. Che...
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Organometallics 2009, 28, 2195–2205

2195

Coordinating Tectons: Bipyridyl-Terminated Group 8 Alkynyl Complexes George A. Koutsantonis,* Gareth I. Jenkins, Phil A. Schauer, Barbara Szczepaniak, Brian W. Skelton, Colin Tan, and Allan H. White Chemistry, School of Biomedical, Biomolecular and Chemical Sciences, UniVersity of Western Australia, 35 Stirling Highway, Crawley, WA, 6009 Australia ReceiVed October 15, 2008

The pendant bipyridyl moiety of transition metal σ-acetylide complexes incorporating the 5-ethynyl2,2′-bipyridine moiety provides a site of chelation for additional metal centers and facile access to multinuclear complexes as model systems for organometallic “molecular wires”. The mononuclear complexes [CpRu(CO)2(C2bpy)] (Cp ) C5H5, C5Me5) and [RuCl(P∩P)2(C2bpy)] (P∩P ) dppm, dppe) have been synthesized and characterized through spectroscopic means, providing context for the synthesis and spectroscopic characterization of the heterometallic coordination complex [RuCl(dppe)2(C2bpy-κ2N,N′-PdCl2)]. A number of the complexes were further characterized by solid-state X-ray structural determinations. These studies were extended to other metal ligand systems, and the structures of the tris-bidentate ruthenium(II) complex [Ru(bpy)2(5-ethynyl-2,2′-bipyridine)](PF6)2 and gold(I) σ-alkynyl complexes [(PR3)Au(C2bpy)] (PR3 ) PEt3, PPh3) are reported. Introduction The physical limitations of metal wire as connectors in electronic devices will soon be reached, and thus we require alternatives that will be effective in molecular devices suited to the new era of computing. The approach has been to devise so-called “molecular wires” that comprise delocalizable bridges that are capable of carrying charge.1-4 Our approach is to combine coordination and, its subset, organometallic chemistry to produce organometallic coordination polymers. This has the advantage of a well-developed chemistry defining the sites of coordination and stabilization of metal centers with the malleability of organometallic conjugated ligands. Our first efforts that utilized transition metal allenylidenes5 seemed to fulfill all the criteria. We targeted heterocyclic ketones to provide the coordinating functionality required and initially targeted 4,5-diazafluoren-9-one to make the corresponding bipyridyl-substituted allenylidene complexes. Bis-diphosphine metal complexes were attractive given they had potential for the formation of ditopic coordinating allenylidene tectons, although we, and others, have yet to find a general route to these. Thus, we have targeted systems that are potentially neutral to provide models for molecular wires and potential electrochemical switches. Here we report the synthesis and characterization of a series of bipyridyl-substituted alkynyl complexes of a series of metals.

cells), and spectra acquired on a DigiLab Excalibur FTS-3000 spectrometer. UV-vis spectra were obtained using a HP-8452A diode-array spectrophotometer from solutions in quartz cuvettes. 1 H, {1H}13C, and {1H}31P nuclear magnetic resonance spectra were acquired on Bruker ARX-300, Bruker AV-600, or Varian-400 spectrometers and referenced with respect to residual solvent signals or an external capillary of 85% H3PO4 for 31P NMR spectra. Mass spectra were acquired on a VG Autospec spectrometer employing the fast-atom-bombardment (FAB) or electrospray (ES) techniques. Elemental analyses were performed by Microanalytical Services, Research School of Chemistry, Australian National University, Canberra, Australia. Cyclic voltammetry measurements were performed on an ADInstruments Maclab/4e interface and Maclab potentiostat (1 mm diameter Pt disk working, Pt auxiliary, and Ag/ AgCl reference mini-electrode). Solutions contained 0.1 M [nBu4N]PF6 and 5-10 mM complex in CH2Cl2 and were purged and maintained under an atmosphere of argon. Scan rates were 100 mV s-1 and referenced to the internal [FcH]/[FcH]+ couple (E1/2 ) +560 mV, ∆Ep ) 70 mV). Solvents for chromatography and general workup procedures were distilled prior to use, while solvents for anaerobic reactions were dried and purified by appropriate means6 prior to distillation and storage under an atmosphere of high-purity argon. The compounds [(PEt3)Au(C2bpy)] (7), [(PPh3)Au(C2bpy)] (8),7 cis[RuCl2(dppm)2], cis-[RuCl2(dppe)2],8 [PdCl2(PhCN)2],9 [CpRuCl(CO)2],10 [Cp*RuCl(CO)2],11 [Ru(bpy)2(HC2bpy)](PF6)2 (9),12

Experimental Section General Considerations. Samples for infrared spectroscopy were prepared as Nujol mulls (NaCl plates) or as CH2Cl2 solutions (CaF2 * Corresponding author. E-mail: [email protected]. Fax: +61 8 64887247. (1) Lindsay, S. Faraday Discuss. 2006, 131, 403–409. (2) James, D. K.; Tour, J. M. Top. Curr. Chem. 2005, 257, 33–62. (3) Otsubo, T.; Aso, Y.; Takimiya, K. Bull. Chem. Soc. Jpn. 2001, 74, 1789–1801. (4) Barigelletti, F.; Flamigni, L. Chem. Soc. ReV. 2000, 29, 1–12. (5) Cifuentes, M. P.; Humphrey, M. G.; Koutsantonis, G. A.; Lengkeek, N. A.; Petrie, S.; Sanford, V.; Schauer, P. A.; Skelton, B. W.; Stranger, R.; White, A. H. Organometallics 2008, 27, 1716–1726.

(6) Armarego, W. L. F.; Chai, C. L. L. Purification of Laboratory Chemicals, 5th ed.; Butterworth-Heinemann, 2003. (7) Vicente, J.; Gil-Rubio, J.; Barquero, N.; Jones, P. G.; Bautista, D. Organometallics 2008, 27, 646. (8) Chaudret, B.; Commenges, G.; Poilblanc, R. J. Chem. Soc., Dalton Trans. 1984, 1635–1639. (9) Anderson, G. K.; Lin, M. Inorg. Synth. 1990, 28, 60–63. (10) Eisenstadt, A.; Tannenbaum, R.; Efraty, A. J. Organomet. Chem. 1981, 221, 317. (11) Fagan, P. J.; Mahoney, W. S.; Calabrese, J. C.; Williams, I. D. Organometallics 1990, 9, 1843. (12) Vra´bel, M.; Hocek, M.; Havran, L.; Fojta, M.; Votruba, I.; Klepeta´øova´, B.; Pohl, R.; Rulı´sˇek, L.; Zendlova´, L.; Hobza, P.; Shih, I.h.; Mabery, E.; Mackman, R. Eur. J. Inorg. Chem. 2007, 1752.

10.1021/om800992p CCC: $40.75  2009 American Chemical Society Publication on Web 03/19/2009

2196 Organometallics, Vol. 28, No. 7, 2009 [RuCl(dppm)2(C2Ph)],13 and HC2bpy14 were synthesized by published methods, while remaining reagents were obtained from commercial suppliers and used as received. Neutral Al2O3 (Fluka) for chromatography was deactivated to “Brockman activity II” by the standard protocol.6 All reactions were performed under an atmosphere of high-purity argon utilizing standard Schlenk techniques, except where explicitly indicated. [CpRu(CO)2(C2bpy)] (1). [CpRuCl(CO)2] (436 mg, 1.69 mmol) and HC2bpy (306 mg, 1.70 mmol) were suspended in a mixture of NEt3 (100 mL) and thf (20 mL), to which was added CuI (16 mg, 0.085 mmol), and the reaction mixture was stirred at ambient temperature for 70 h. The solution was filtered and taken to dryness by rotary evaporation, and the residue then redissolved in CH2Cl2 and adsorbed onto Al2O3. Elution with 1:1 EtOAc/hexanes afforded a bright yellow fraction, which was taken to dryness by rotary evaporation and recrystallized from CH2Cl2/pentanes to yield the pure product as orange crystals (359 mg, 0.894 mmol, 52.9%). Anal. Calcd for C19H12N2O2Ru1: C, 56.86; H, 3.01; N, 6.98. Found: C, 56.62; H, 3.18; N, 6.96. 1H NMR (300 MHz, CD2Cl2): δ (ppm) 8.62 (ddd, 1H, H6′), 8.54 (dd, 1H, H6), 8.37 (m, 1H, H3′), 8.27 (dd, 1H, H3), 7.79 (ddd, 1H, H4′), 7.67 (dd, 1H, H4), 7.26 (ddd, 1H, H5′), 5.51 (s, 5H, Cp). {1H}13C NMR (75.5 MHz, CD2Cl2): δ (ppm) 197.3 (s, CO), 156.3 (s, C2′), 152.3 (s, C2), 151.9 (s, C6), 149.4 (s, C6′), 139.0 (s, C4), 137.0 (s, C4′), 124.9 (s, C5), 123.6 (s, C5′), 121.0 (s, C3′), 120.2 (s, C3), 107.6 (s, Cβ), 91.6 (s, CR), 88.6 (s, Cp). IR (cm-1): νCtC 2128 (s), νCdO 2040 (vs), and 1990 (vs). FAB+-MS (CH2Cl2): m/z 403 ([M + H]+), 375 ([M + H CO]+), 347 ([M + H - (CO)2]+). [Cp*Ru(CO)2(C2bpy)] (2). [Cp*RuCl(CO)2] (89 mg, 0.27 mmol) and HC2bpy (49 mg, 0.27 mmol) were dissolved in NEt3 (20 mL), to which was added CuI (2.6 mg, 0.014 mmol), and the reaction mixture was stirred at ambient temperature overnight. The solution was filtered and taken to dryness by rotary evaporation,and the residue then redissolved in CH2Cl2 and adsorbed onto Al2O3. Elution with 1:1 EtOAc/hexanes afforded a bright yellow fraction, which was taken to dryness by rotary evaporation and recrystallized from Et2O/pentanes to yield the pure product as orange crystals (63.7 mg, 0.14 mmol, 50%). Anal. Calcd for C24H22N2O2Ru: C, 61.13; H, 4.70; N, 5.94. Found: C, 61.34; H, 4.78; N, 5.94. 1H NMR (300 MHz, CD2Cl2): δ (ppm) 8.62 (ddd, 1H, H6′), 8.57 (dd, 1H, H6), 8.36 (m, 1H, H3′), 8.26 (dd, 1H, H3), 7.79 (m, 1H, H4′), 7.67 (dd, 1H, H4), 7.25 (ddd, 1H, H5′), 2.03 (s, 15H, C5Me5). {1H}13C NMR (125 MHz, CD2Cl2): δ (ppm) 200.2 (s, CO), 156.4 (s, C2′), 151.8 (s, C2), 151.8 (s, C6), 149.4 (s, C6′), 138.7 (s, C4), 137.0 (s, C4′), 125.6 (s, C5), 123.5 (s, C5′), 120.9 (s, C3′), 120.2 (s, C3), 108.5 (s, CR), 105.1 (s, Cβ), 101.4 (s, C5Me5), 10.4 (C5Me5). IR (cm-1): νCtC 2110 (s), νCdO 2029 (vs), and 1975 (vs). FAB+MS (CH2Cl2): m/z 473 ([M + H]+), 416 ([M - (CO)2]+). [RuCl(dppm)2(C2bpy)] (3). A flask charged with AgPF6 (235 mg, 0.929 mmol) and cis-[RuCl2(dppm)2] (122 mg, 0.126 mmol) was covered in foil to exclude light and CH2Cl2 (50 mL) added. The mixture was stirred at ambient temperature for 15 h. The resulting bright yellow suspension was transferred by cannula to a short column of Celite (ca. 5 g) and filtered directly into a solution of HC2bpy (30 mg, 0.17 mmol) and DBU (85 µL, 0.57 mmol) in CH2Cl2 (10 mL). The column of Celite was washed with additional CH2Cl2 (5 × 10 mL), and the resulting reaction mixture stirred at ambient temperature for a further 2 h, yielding a bright yellow suspension. The reaction mixture was then opened to the atmosphere and filtered through a short column of Al2O3, eluting with CH2Cl2 to yield a bright yellow solution, from which solvent was removed by rotary evaporation. The bright yellow residue was washed with hexanes (3 × 100 mL) and recrystallized from boiling toluene to (13) Touchard, D.; Haquette, P.; Pirio, N.; Toupet, L.; Dixneuf, P. H. Organometallics 1993, 12, 3132. (14) Grosshenny, V.; Romero, F. M.; Ziessel, R. J. Org. Chem. 1997, 62, 1491.

Koutsantonis et al. afford the pure product as bright yellow needles (94 mg, 0.087 mmol, 69%). Anal. Calcd for C62H51Cl1N2P4Ru1: C, 68.66; H, 4.74; N, 2.58. Found: C, 68.16; H, 4.65; N, 3.08. 1H NMR (600 MHz, CDCl3): δ (ppm) 8.634 (ddd, 1H, H6′), 8.248 (ddd, 1H, H3′), 7.877 (dd, 1H, H3), 7.754 (ddd, 1H, H4′), 7.514 (dd, 1H, H6), 7.51-5.47 (m, 8H, Hortho), 7.46-7.42 (m, 8H, Hortho), 7.32-7.24 (m, 8H, Hpara), 7.22-7.14 (m, 9H, Hmeta and H5′), 7.13-7.09 (m, 8H, Hmeta), 6.231 (dd, 1H, H4), 4.950 (quintet, 4H, PCH2P). {1H}13C NMR (151 MHz, CDCl3): δ (ppm) 156.983 (s, C2′), 150.389 (s, C6), 149.152 (s, C6′), 148.943 (s, C2), 137.900 (s, C4), 136.771 (s, C4′), 134.862 (quintet, Cipso), 134.156 (quintet, Cipso), 133.839 (s, Cortho), 133.410 (s, Cortho), 129.497 (s, Cpara), 129.416 (s, Cpara), 127.718 (s, Cmeta), 127.708 (s, Cmeta), 127.301 (s, C5), 122.568 (s, C5′), 120.696 (s, C3′), 119.612 (s, C3), 110.019 (s, Cβ), 50.466 (quintet, PCH2P) (CR not identified). {1H}31P NMR (243 MHz, CDCl3): δ (ppm) -6.011 (s, dppm). IR (cm-1): νCtC 2068 (vs). UV-vis (MeCN) λ (nm) [ × 104 M-1 cm-1]: 228 [6.57], 268 [4.08], 386 [2.38]. [RuCl(dppe)2(C2bpy)] (4). A flask charged with AgPF6 (375 mg, 1.48 mmol) and cis-[RuCl2(dppe)2] (148 mg, 0.153 mmol) was covered in foil to exclude light, and CH2Cl2 (50 mL) was added. The mixture was stirred at ambient temperature for 16 h. The resulting bright yellow suspension was transferred by cannula to a short column of Celite (ca. 5 g) and filtered directly into a solution of HC2bpy (30 mg, 0.17 mmol) and DBU (70 µL, 0.47 mmol) in CH2Cl2 (10 mL). The column of Celite was washed with additional CH2Cl2 (5 × 10 mL), and the resulting reaction mixture was stirred at ambient temperature for a further 3 h, yielding a bright orange suspension. The reaction mixture was then opened to the atmosphere and filtered through a short column of Al2O3, eluting with CH2Cl2, to yield a bright yellow solution, from which solvent was removed by rotary evaporation to give the pure product as a bright yellow powder (95 mg, 0.085 mmol, 56%). Anal. Calcd for C64H55Cl1N2P4Ru1: C, 69.09; H, 4.98; N, 2.52. Found: C, 68.58; H, 5.08; N, 2.53. 1H NMR (400 MHz, CDCl3): δ (ppm) 8.650 (ddd, 1H, H6′), 8.316 (ddd, 1H, H3′), 8.074 (dd, 1H, H3), 7.987 (dd, 1H, H6), 7.780 (ddd, 1H, H4′), 7.44-7.35 (m, 16H, Hortho), 7.25-7.15 (m, 9H, Hpara and H5′), 7.06-7.00 (m, 8H, Hmeta), 6.99-6.95 (m, 8H, Hmeta), 6.770 (dd, 1H, H4), 2.8-2.6 (m, 8H, P(CH2)2P). {1H}13C NMR (100 MHz, CDCl3): δ (ppm) 156.797 (s, C2′), 150.419 (s, C6), 149.296 (s, C2), 149.172 (s, C6′), 137.730 (s, C4), 136.813 (s, C4′), 136.037 (quintet, Cipso), 135.749 (quintet, Cipso), 134.551 (t, Cortho), 134.089 (t, Cortho), 129.063 (s, Cpara), 127.337 (s, Cmeta), 127.142 (s, Cmeta), 126.947 (s, C5), 122.699 (s, C5′), 120.719 (s, C3′), 119.938 (s, C3), 110.913 (s, Cβ), 30.655 (quintet, P(CH2)2P) (CR not identified). {1H}31P NMR (243 MHz, CDCl3): δ (ppm) 49.632 (s, dppe). IR (cm-1): νCtC 2061 (s). FAB+MS (CH2Cl2): m/z 1112 (25%, [M]+), 1077 (26%, [M - Cl]+), 897 (29%, [M - Cl - C2bpy]+). UV-vis (MeCN) λ (nm) [ × 104 M-1 cm-1]: 208 [8.83], 226 [5.36], 257 [4.00], 389 [2.15]. [RuCl(dppe)2(C2bpy-K2-N,N′-PdCl2)] (5). [PdCl2(PhCN)2] (25 mg, 0.064 mmol) was added to a solution of [RuCl(dppe)2(C2bpy)] (62 mg, 0.056 mmol) in MeCN (70 mL). The solution was stirred at ambient temperature for an hour, over which time a dark red powder deposited from the bright red solution. The solvent volume was reduced to ca. 10 mL in vacuo, and the supernatant decanted by filter-tipped cannula. The residue was washed with Et2O (2 × 10 mL) and recrystallized from 1:5 CH2Cl2/Et2O to yield the product as blood red crystals (34 mg, 0.026 mmol, 47%). Anal. Calcd for C64H55Cl3N2P4Pd1Ru1 · 3CH2Cl2: C, 52.10; H, 3.98; N, 1.81. Found: C, 51.71; H, 4.40; N, 2.10. 1H NMR (600 MHz, CD2Cl2): δ (ppm) 9.305 (ddd, 1H, H6′), 8.650 (dd, 1H, H6), 8.016 (ddd, 1H, H4′), 7.765 (ddd, 1H, H3′), 7.59-7.54 (m, 8H, Hortho), 7.45-7.41 (m, 2H, H5′ and H3), 7.30-7.26 (m, 4H, Hpara), 7.26-7.22 (m, 4H, Hpara), 7.17-7.12 (m, 8H, Hortho), 7.12-7.08 (m, 8H, Hmeta), 7.06-7.02 (m, 8H, Hmeta), 6.262 (dd, 1H, H4), 2.80-2.70 (m, 8H, P(CH2)2P). {1H}13C NMR (100 MHz, CD2Cl2): δ (ppm) 157.640 (s, C2′), 151.779 (s, C6), 150.730 (s, C6′), 148.119 (s, C2), 140.954

Coordinating Tectons (s, C4), 139.986 (s, C4′), 136.103 (quintet, Cipso), 135.667 (quintet, Cipso), 134.993 (s, Cortho), 133.846 (s, Cortho), 129.883 (s, C5), 129.754 (s, Cpara), 129.604 (s, Cpara), 127.917 (s, Cmeta), 127.594 (s, Cmeta), 125.003 (s, C5′), 121.379 (s, C3′), 121.136 (s, C3), 113.424 (s, Cβ), 30.793 (quintet, P(CH2)2P) (CR not identified). {1H}31P NMR (243 MHz, CD2Cl2): δ (ppm) 48.285 (s, dppe). IR (cm-1): νCtC 2025 (vs). ES+-MS (CH2Cl2): m/z 1254 (18%, [M - Cl]+), 1115 (100%, [M - PdCl2]+). UV-vis (CH2Cl2) λ (nm) [ × 104 M-1 cm-1]: 258 [4.10], 306sh [1.15], 516 [1.81]. Reaction of [RuCl(dppm)2(C2Ph)] with HC2bpy. [RuCl(dppm)2(C2Ph)] (81 mg, 0.080 mmol) and HC2bpy (23 mg, 0.13 mmol) were dissolved in a mixture of CH2Cl2 (30 mL) and NEt3 (250 µL, 1.8 mmol), to which was added solid NaPF6 (50 mg, 0.30 mmol). The yellow suspension was stirred overnight at ambient temperature, then filtered through a pad of Celite, and volatile substances were removed by rotary evaporation. The orange residue was redissolved in a minimum amount of CH2Cl2 and chromatographed on a short column of Al2O3 utilizing CH2Cl2/hexanes as the mobile phase. The bright yellow fraction was collected and taken to dryness by rotary evaporation to yield the crude product mixture as a bright yellow powder (78 mg). Slow evaporation of a PhMe solution of the mixture yielded crystals of trans-[Ru(dppe)2(C2Ph)(C2bpy)] (6) suitable for X-ray diffraction analysis. Structure Determinations. CCD area-detector diffractometer data were measured (ω-scans; monochromatic Mo KR λ ) 0.71073 Å or Cu KR λ ) 1.54184 Å, yielding Nt(otal) reflections, these merging to N unique (Rint cited) after multiscan (1, 2, 4, 7, 8, and 9) or analytical (5 and 6) absorption correction (proprietary software), No with I > 2σ(I) considered “observed”). All reflections were used in the full matrix least-squares refinement on F2, refining anisotropic displacement parameter forms for the non-hydrogen atoms (exceptions: 5 solvent C atoms, 6 one solvent toluene), hydrogen atom treatment following a riding model (reflection weights: σ2(Fo2) + (aP)2 + (bP)-1 (P ) (Fo2 + 2Fc2)/3)). Neutral atom complex scattering factors were employed within the SHELXL 97 program.15 Pertinent results are given in the text, tables, and figures, the latter showing non-hydrogen atoms with 20% (room temperature) or 50% (“low” temperature) probability amplitude displacement envelopes, hydrogen atoms having an arbitrary radius of 0.1 Å.

Results and Discussion Syntheses of Cyclopentadienylruthenium(II) Derivatives. We have found that the CpRu(CO)2 moiety is extremely flexible in its mode of coordination and has allowed us to investigate a number of unusual16-23 bonding situations. Thus, we first decided to attempt the formation of mono-alkynyl complexes to provide suitable models for the formation of oligomeric complexes. The presence of only one bipyridyl moiety enables the selective coordination of another metal to the bipyridyl group and should allow the investigation of the effects of alterations (15) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122. (16) Griffith, C. S.; Koutsantonis, G. A.; Raston, C. L.; Selegue, J. P.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 1996, 518, 197–202. (17) Byrne, L. T.; Griffith, C. S.; Hos, J. P.; Koutsantonis, G. A.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 1998, 565, 259–265. (18) Byrne, L. T.; Hos, J. P.; Koutsantonis, G. A.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 2000, 598, 28–35. (19) Byrne, L. T.; Hos, J. P.; Koutsantonis, G. A.; Sanford, V.; Skelton, B. W.; White, A. H. Organometallics 2002, 21, 3147–3156. (20) Griffith, C. S.; Koutsantonis, G. A.; Skelton, B. W.; White, A. H. Chem. Commun. 2002, 2174–2175. (21) Griffith, C. S.; Koutsantonis, G. A.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 2003, 670, 198–204. (22) Griffith, C. S.; Koutsantonis, G. A.; Skelton, B. W.; White, A. H. Angew. Chem., Int. Ed. 2005, 44, 3038–3043. (23) Griffith, C. S.; Koutsantonis, G. A.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 2005, 690, 3410–3421.

Organometallics, Vol. 28, No. 7, 2009 2197 Scheme 1. Synthesis of the Cyclopentadienylruthenium(II) σ-Alkynyl Complexes

to the electronic structure and steric bulk surrounding the metal centers on the electronic properties of the complexes formed. Close examination of the resulting spectroscopic, structural, and electronic properties of such derivatives may also provide an insight into the nature of the metal-alkynyl bonding. Following the synthetic protocol for the synthesis of [CpFe(CO)2(C2Ph)],24 the analogous ruthenium complexes [CpRu(CO)2(C2bpy)] (1) and [Cp*Ru(CO)2(C2bpy)] (2) were readily obtained by the CuI-catalyzed reaction of the metal halide with 5-ethynyl-2,2′-bipyridine in NEt3 (Scheme 1). The air-stable crystalline solids were readily isolated as pure compounds and fully characterized by standard techniques. Attempts to extend this synthetic protocol to the synthesis of [CpFe(CO)2(C2bpy)] were unsuccessful, with varied reaction times and cosolvents leading only to the recovery of starting materials in addition to a variety of decomposition products not incorporating the bipyridine moiety. Although both complexes 1 and 2 were air stable in the solid state, they slowly decomposed in solution, forming an unidentified brown oil. Decomposition products were easily removed by filtration through alumina with subsequent recrystallization from degassed solutions. The decomposition accounts for the relatively low yields obtained, although yields as high as 64% were obtained when the reaction was carried out on a smaller scale, which allowed the product to crystallize from the reaction mixture. Characterization of the Cyclopentadienylruthenium(II) Derivatives. In infrared spectra the weak alkynyl absorbance of the free ligand (2097 cm-1) shifted to a strong alkynyl absorbance at 2128 and 2110 cm-1 in 1 and 2, respectively, indicating the formation of a σ-bound metal alkynyl. Two strong absorbances at 2040 and 1990 cm-1 for 1 and 2029 and 1975 cm-1 for 2 are assigned to the symmetric and asymmetric carbonyl stretching process, the in-phase mode vibrating at higher frequency.25 The energies of infrared absorbances for the Cp* complex 2 are lower relative to complex 1, consistent with increased π-back-bonding on account of greater electron density at the metal center.26 The FAB mass spectra of the two complexes contained peaks at m/z 403 and 473 corresponding to the [(1)+H]+ and [(2)+H]+ molecular ions, respectively. Ions corresponding to the loss of both carbonyl groups were detected in both complexes, with an intermediate loss of one carbonyl group detected for 2. The 1H NMR spectra of the two complexes exhibit single resonances for the cyclopentadienide groups, at 5.51 ppm for 1 and 2.03 ppm for 2, while the bipyridyl protons of both complexes are in similar environments, as demonstrated by the nearly identical spectra. Relative to the free ligand, the 1H NMR spectroscopy resonances of the coordinated σ-alkynyl moiety all exhibit an upfield shift, most notably in the pyridyl ring (24) Bruce, M. I.; Humphrey, M. G.; Matisons, J. G.; Roy, S. K.; Swincer, A. G. Aust. J. Chem. 1984, 37, 1955. (25) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 4th ed.; John Wiley & Sons: New York, 1980. (26) Manna, J.; John, K. D.; Hopkins, M. D. AdV. Organomet. Chem. 1995, 38, 78–154.

2198 Organometallics, Vol. 28, No. 7, 2009

Figure 1. Molecular projection of complex 1. Selected bond lengths (Å) and angles (deg): Ru-C(1) 2.0104(16), Ru-C(10) 1.8863(19), Ru-C(20) 1.8875(19), C(1)-C(2) 1.209(2), C(2)-C(15) 1.433(2), C(10)-Ru-C(20)90.28(8),Ru-C(1)-C(2)178.19(15),C(1)-C(2)C(15) 178.41(19).

Figure 2. Molecular projection of complex 2. Selected bond lengths (Å) and angles (deg): Ru-C(1) 2.066(4), Ru-C(10) 1.916(4), Ru-C(20) 1.919(4), C(1)-C(2) 1.234(6), C(2)-C(15) 1.451(6), C(10)-Ru-C(20) 91.71(17), Ru-C(1)-C(2) 174.7(3), C(1)-C(2)C(15) 176.8(5).

closest to the ruthenium center. Resonances in {1H}13C NMR spectra were unequivocally assigned via 1H,13C-HSQC and HMBC experiments, with resonances attributed to CR, Cβ, and C5 considerably deshielded relative to the free ligand on account of metal-carbon bond formation. The CR resonances of 1 (91.6 ppm) and 2 (108.5 ppm) appear at different frequencies, suggesting the ancillary ligands surrounding the metal affect the environment of the alkynyl bridge, but the nature of this effect is unclear. The resonances due to Cβ in the two complexes are at similar frequencies (107.6 ppm for 1 and 105.1 ppm for 2). In the absence of the two-dimensional experiments, assignment of these signals is problematic,27 and arguments based on the electronic environments of the two complexes, or comparisons to related compounds, would likely have drawn incorrect conclusions, as the resonance frequencies of the alkynyl carbons are seen to be strongly dependent on the metal environment. Comprehensive tabulations of alkynyl 13C NMR chemical shifts also illustrate this point.27 The remaining singlet, downfield resonance was readily assigned to the coordinated carbonyl ligands (197.3 ppm 1; 200.2 ppm 2), and similarly, the singlet upfield resonances of the cyclopentadienide ligands (88.6 ppm 1; 101.4 and 10.4 ppm 2). Single-Crystal X-Ray Structure Determinations of Complexes 1 and 2. Crystals of 1 and 2 suitable for X-ray structure determination were produced by careful addition of n-pentane to a dichloromethane solution of 1 and an ethereal solution of 2. The solid-state structures are depicted in Figures 1 and 2, respectively. The Cp derivative 1 crystallized in the centrosymmetric P21/n space group, with four molecules comprising the monoclinic unit cell, while 2, with the bulkier Cp* moiety, (27) Wrackmeyer, B.; Horchler, K. Prog. Nucl. Magn. Reson. Spectrosc. 1990, 22, 209–253.

Koutsantonis et al.

crystallized with a noncentrosymmetric P212121 space group, forming an orthorhombic unit cell consisting of four molecules. The crystal structures are unremarkable and similar to those of other transition metal alkynyl complexes.26 The molecular representations confirm the expected transoid conformation of the bipyridyl moiety in the solid state, with a skewed arrangement. The pyridyl interplanar angles deviate from a truly trans planar conformation by 24.44(6)° in 1 and 12.8(1)° in 2, respectively. The smaller interplanar angle in the permethylated derivative 2 may be due to increased intermolecular steric repulsions in the solid state. As alluded to in the previous discussion, comparisons of spectroscopic and crystallographic data in order to gain insights into the bonding in metal-alkynyl compounds, in particular, consideration of the effects of RufCtC-bpy π-back-bonding, often lead to conflicting conclusions. The use of alkynyl infrared stretching frequencies and crystallographic data of metal σ-alkynyls has been reviewed,26 together with the use of molecularorbital calculations and photoelectron spectroscopy. Theoretical studies28-30 suggest that π-back-bonding is minimal in related [CpFe(CO)2(CtCR)] and [CpFe(dppe)(CtCR)] complexes; however it can be increased by addition of electron-withdrawing substituents on the alkynyl.28 The related σ-butadiynyl metal complexes are believed to have greater metal-alkynyl π-interactions.31 The use of magnetic resonance spectroscopy in the elucidation of the bonding and structure of metal alkynyls has also been reviewed.27 In the absence of detailed molecular modeling and synthesis of a larger range of related complexes the effects of π-back-bonding are difficult to gauge; however these matters need to be addressed in order to assess the potential for these complexes as molecular wires. Syntheses of Bis(diphosphine)ruthenium(II) Derivatives. Attempts to synthesize bis(diphosphine)ruthenium(II) alkynyl complexes incorporating the bipyridine moiety met with significant difficulties presumably, as a consequence of the unique complications arising from the basicity of 5-ethynyl-2,2′bipyridine. The most facile synthesis of [RuCl(P∩P)2(C2R)] complexes is depicted below in Scheme 2, involving deprotonation of an intermediate vinylidene complex [RuCl(P∩P)2d CdC(H)R]+ formed by activation of the terminal alkyne HC2R at the coordinatively unsaturated [RuCl(P∩P)2]+ intermediate (formed in situ by halide abstraction from [RuCl2(P∩P)2] with NaPF6 or a similar reagent).32 The advantage of this route is the ability to isolate the vinylidene complex from excess alkyne and the halide-abstraction agent, thus allowing ready isolation of the mono-alkynyl complex without complications arising from further reaction with excess reactants. Alternately, combination of the halide-abstracting agent, alkyne ligand, and base in a one-pot reaction should readily afford the bis-alkynyl complex. Following this synthetic protocol, reaction of cis-[RuCl2(dppm)2] with a single equivalent of HC2bpy, mediated by NaPF6 in dichloromethane, led to the rapid appearance of a dark maroon color in solution, characteristic of the vinylidene complex. Analysis of the crude reaction product indicated the presence of the targeted vinylidene complex in addition to the (28) Costuas, K.; Paul, F.; Toupet, L.; Halet, J.-F.; Lapinte, C. Organometallics 2004, 23, 2053–2068. (29) Lichtenberger, D. L.; Renshaw, S. K.; Bullock, R. M. J. Am. Chem. Soc. 1993, 115, 3276–3285. (30) Kostic´, N. M.; Fenske, R. F. Organometallics 1982, 1, 974. (31) Lichtenberger, D. L.; Renshaw, S. K. Organometallics 1993, 12, 3522. (32) Haquette, P.; Pirio, N.; Touchard, D.; Toupet, L.; Dixneuf, P. H. J. Chem. Soc., Chem. Commun. 1993, 163.

Coordinating Tectons Scheme 2. General Synthesis of Bis(diphosphine)ruthenium(II) Mono- and Bis-alkynyl Complexes via Activation of a Terminal Alkynea

Organometallics, Vol. 28, No. 7, 2009 2199 Scheme 3. Synthesis of the Mono-alkynyl Complexes

utilizing AgPF6 as the halide abstraction agent (Scheme 3). Attempts to synthesize the dppe-ligated analogue (4) were frustrated by the same synthetic difficulties described above for the dppm ligated complex; however it was also possible to isolate the mono-alkynyl in a pure form in 56% yield through application of the same two-step AgPF6-mediated route.

a Conditions: i ) HCtCR, MX; ii ) NEt , DBU, etc.; MX ) NaPF , 3 6 NaBF4, etc.

mono- and bis-alkynyl complexes as well as unreacted [RuCl2(dppm)2]. As also noted in the synthesis of [CpRu(L)2(C2bpy)] (L ) PPh3, 1/2 dppf),33 the 5-ethynyl-2,2′-bipyridine proligand is often sufficiently basic to deprotonate the intermediate vinylidene complex, thus forming an equilibrium between the vinylidene and alkynyl complexes in addition to (bi)pyridinium cations. When such an equilibrium incorporates the complex [RuCl(dppm)2(C2bpy)], abstraction of the additional chloride incorporates the trans-bis-alkynyl and -vinylidene complexes within the equilibrium, thus preventing direct synthesis of the targeted mono-alkynyl complex. A large number of reaction conditions were examined in an attempt to access exclusively the mono-alkynyl complex; however reaction products were invariably a mixture of the mono- and bis-alkynyl complexes. Column chromatography on neutral alumina (activity II or III) leads invariably to coelution of the mono- and bis-alkynyl complexes in addition to any of the [RuCl2(dppm)2] precursor, while attempts to chromatograph product mixtures on neutral alumina (activity I), basic alumina, silica gel, or Florosil led to extensive decomposition. As the formation of the bis-alkynyl complex requires halide abstraction from the [RuCl(dppm)2(C2bpy)] complex, attempts were made to separate the halide abstraction reactant NaPF6 from the alkyne. Consequently cis-[RuCl2(dppm)2] and NaPF6 were reacted to form the [RuCl(dppm)2]+ intermediate, and the resulting solution was filtered through a large pad of Celite directly into a solution of HC2bpy and base. Unfortunately these conditions still resulted in isolation of the mono-alkynyl complex contaminated by up to 10% of the bis-alkynyl complex, presumably the result of marginal solubility of NaPF6. Eventually the targeted mono-alkynyl (3) was isolated in a pure form in 69% yield by applying a similar two-step methodology (33) Packheiser, R.; Ecorchard, P.; Walfort, B.; Lang, H. J. Organomet. Chem. 2008, 693, 933.

Having successfully isolated the mono-alkynyl complexes, investigations were undertaken to determine the ability of the pendant bipyridyl moiety to coordinate additional metal fragments. The reaction of 4 with [PdCl2(PhCN)2] was envisaged to proceed in a facile manner by displacement of the labile benzonitrile ligands in preference for chelation of the bipyridyl metallo-ligand. Satisfactorily, combination of equimolar quantities of the two reactants in acetonitrile solution under mild conditions leads to the precipitation of the target complex [RuCl(dppe)2(C2bpy-κ2-N,N′-PdCl2)] (5) as the pure complex in 47% yield. Despite the fact that syntheses of the mono-alkynyl complexes were confounded by the facile formation of the bis-alkynyl analogue, selectively targeting the synthesis and isolation of the bis-alkynyl complex was not trivial. Although the reaction of cis-[RuCl2(P∩P)2] with excess alkyne and halide abstraction agent readily forms the bis-alkynyl complex, it was not possible to drive this reaction to completion under a variety of standard reaction conditions employing NaPF6 or AgPF6 with DBU or NEt3 in halocarbon solvents. Although product mixtures were readily synthesized with a large excess of the bis-alkynyl complex, 5-20% of the mono-alkynyl was also present in addition to excess HC2bpy and isomerized trans-[RuCl2(P∩P)2]. Extended reaction times and/or prolonged heating led to decomposition of the reaction mixture with no significant difference in product ratios; hence the equilibrium between the mono- and bis-alkynyl complexes (in addition to the intermediate alkynyl-vinylidene complex) is not readily driven to completion under these standard conditions. Investigations were consequently undertaken to explore alternate reaction conditions to access the targeted bis-alkynyl complexes, including the use of AgPF6, KOtBu/thf-CH2Cl2, NaOMe/MeOH-CH2Cl2, Na2CO3/ NaPF6/CH2Cl2, or SnO2/CH2Cl2; however these additional homogeneous and heterogeneous routes also failed to yield the bis-alkynyl complexes in a pure form, more often resulting in significant decomposition of the reaction mixture with very low mass recovery. An efficient direct synthesis of the bis-alkynyl complexes remains elusive, and our investigations continue. In this vein, the mixed-ligand bis-alkynyl complex [Ru(dppm)2(C2Ph)(C2bpy)] was targeted, by reaction of [RuCl(dppm)2(C2Ph)] with HC2bpy in the presence of NaPF6 and NEt3 (Scheme 4). The isolated product mixture was, remarkably, a mixture of trans-[RuCl2(dppm)2], both mono-alkynyl complexes, and both symmetrical bis-alkynyl complexes, with the targeted asymmetric complex (6) accounting for only ca. 60% of the isolated material. Although ligand scrambling has been reported in the synthesis of asymmetrical bis-alkynyl complexes prepared

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Scheme 4. Synthesis of the Asymmetric Bis-alkynyl Complex 6 in a Product Mixture Containing Numerous Scrambling Products (Y, Z ) Cl, C2Ph, C2bpy)

by this route,34,35 or even by reaction of mono-alkynyl complexes with Me3SnC2R36 or LiC2R precursors,37 these previous reports have only ever identified the presence of one of the possible symmetrical bis-alkynyl products, in contrast to the presence of all possible products as witnessed in this case. The nature and degree of the scrambling witnessed is related to the nature of both the coordinated alkynyl and free alkyne proligand, wherein the scrambling mechanism is reliant on competitive dissociation of the chloride or alkynyl ligands from the [RuCl(dppm)2(C2R)] reactant. As evinced by the presence of trans-[RuCl2(dppm)2] in the isolated product mixture, it appears in this case that both the phenyl and bipyridyl alkynyl ligands are readily displaced from the ruthenium center under these conditions, the evident lability of the coordinated “C2bpy” moiety potentially the source of the issues described above in attempts to prepare the symmetrical bis-bipyridyl alkynyl complex. Attempts to separate the product mixture by chromatography or fractional crystallization proved unfruitful, although it was possible to isolate a crystal of trans-[Ru(dppm)2(C2Ph)(C2bpy)] (6) by slow evaporation of a toluene solution of the product mixture. Characterization of the Bis(diphosphine)ruthenium(II) Alkynyl Complexes. The expected trans-octahedral configuration of the chloride and alkynyl ligands in complexes 3-5 is readily confirmed by the observation of a solitary singlet resonance in their {1H}31P NMR spectra, the resonances lying marginally downfield of the trans-[RuCl2(P∩P)2] analogue. Resonances in 1H and {1H}13C NMR spectra were readily assigned through a combination of homo- and heteronuclear 2D correlation experiments, although it was not possible to identify a resonance of the alkynyl CR atom either directly or through means of polarization transfer. The most notable feature of both the 1H and {1H}13C NMR spectra is the presence of individual resonances for each group of four phosphanyl phenyl rings pointing toward either the chloride or alkynyl apex of the phosphine-ligand plane, though it was not readily possible to completely differentiate one set from the other. Proton reso(34) McDonagh, A. M.; Whittall, I. R.; Humphrey, M. G.; Hockless, D. C. R.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 1996, 523, 33. (35) Touchard, D.; Haquette, P.; Guesmi, S.; Le Pichon, L.; Daridor, A.; Toupet, L.; Dixneuf, P. H. Organometallics 1997, 16, 3640. (36) Younus, M.; Long, N. J.; Raithby, P. R.; Lewis, J.; Page, N. A.; White, A. J. P.; Williams, D. J.; Colbert, M. C. B.; Hodge, A. J.; Khan, M. S.; Parker, D. G. J. Organomet. Chem. 1999, 578, 198. (37) Dahlenburg, L.; Weiss, A.; Bock, M.; Zahl, A. J. Organomet. Chem. 1997, 541, 465.

nances of the bipyridyl moiety are clearly separated from one another with the 4- and 6-positioned protons of complexes 3 and 4 significantly shielded relative to the free ligand HC2bpy on account of interactions with the ring currents of the overhanging phenyl rings. Likewise in the palladium-coordinated complex 5, the 6 and 6′ protons are strongly deshielded relative to the parent alkynyl complex 4 on account of proximity to the coordinated PdCl2 moiety, the remaining protons also experiencing a marginal deshielding attributable to donation of electron density to the palladium center.38 Infrared spectroscopy shows a strong absorbance at 2068 cm-1 (3) and 2061 cm-1 (4), consistent with the νCtC absorbance of analogous σ-bound alkynyl complexes [RuCl(P∩P)2(C2R)] (P∩P ) dppm, R ) Ph (2075 cm-1), 2-py (2080 cm-1); P∩P ) dppe, R ) Ph (2067 cm-1), p-biphenyl (2071 cm-1)).13,35,36,39 This absorbance is 36 cm-1 lower in energy at 2025 cm-1 for 5, the lower energy attributed to a decrease of triple-bond character on account of withdrawal of electron density to the coordinated palladium moiety. UV-vis spectra (Figure 3) of the complexes are dominated by intense high-energy absorbances below 300 nm, attributed to ILCT transitions of the bipyridyl moiety and phosphanyl ligands, in addition to CT between ruthenium and the phosphanyl ligands.39 Complexes 3 and 4 also exhibit a broad feature at ca. 390 nm interpreted as an MLCT transition to the “CtC-bpy” moiety.36 In 5 this latter absorption is perturbed by the coordinated palladium moiety and red-shifted to 516 nm, consistent with the lower energy of the νCtC infrared absorption. A weak absorption is also evident at ca. 320 nm for 5, plausibly attributable to a palladium-bipyridyl MLCT transition.38 Cyclic voltammetry studies of the alkynyl complexes 3-5 show two oxidation processes, the first of which is a quasireversible process at ca. 550 mV for complexes 3 and 4 ascribed to a RuII/RuIII oxidation couple, as witnessed in analogous complexes (see Younus et al.36 and references therein). This oxidation couple is anodically shifted by ca. 220 mV to 820 mV in the palladium-coordinated derivative 5, consistent with a withdrawal of electron density from the ruthenium center by the palladium-bipyridyl moiety. A second, poorly reversible oxidation process is centered at ca. 1600 mV for all three complexes 3-5 and is not readily assigned. Analogous com(38) Kamath, S. S.; Uma, V.; Srivastava, T. S. Inorg. Chim. Acta 1989, 161, 49. (39) Naulty, R. H.; McDonagh, A. M.; Whittall, I. R.; Cifuentes, M. P.; Humphrey, M. G.; Houbrechts, S.; Maes, J.; Persoons, A.; Heath, G. A.; Hockless, D. C. R. J. Organomet. Chem. 1998, 563, 137.

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Figure 3. UV-vis absorption spectra of the ruthenium acetylide complex 4 and palladium-coordinated derivative 5. Table 1. Crystal Data and Refinement Details of the Complexes 1 formula Mr (Da) cryst syst space group a (Å) b (Å) c (Å) R (°) β (°) γ (°) V (Å3) Dc (g cm-3) Z µ (mm-1) radiation specimen (mm3) Tmin, max 2θmax (deg) Nt N (Rint) No R1 wR2 (a, b) T (K) a

C19H12N2O2Ru 401.38 monoclinic P21/n (#14) 10.5050(10) 11.613(2) 13.989(2)

2a C24H22N2O2Ru 471.51 orthorhombic P212121 (#19) 12.566(3) 12.644(3) 14.315(3)

109.014(3) 1613.5(4) 1.652 4 0.98 Mo KR 0.51, 0.17, 0.13 0.85, 1.00 75 32 023 8470 (0.030) 6515 0.038 0.092 (0.040, 1.07) 150

2274.4(9) 1.377 4 0.71 Mo KR 0.24, 0.20, 0.14 0.68, 1.00 57 19 411 5366 (0.057) 4552 0.042 0.095 (0.053, 0) 150

4 a ,b

5 b ,c

6c,d

C66.30H57.63ClN2P4Ru C65.5H58.1Cl6.1N2P4PdRu C84H72N2P4Ru 1142.77 1420.86 1334.39 monoclinic monoclinic orthorhombic P21/n (#14) I2/a (#15) P212121 (#19) 13.1714(4) 16.9892(5) 9.60350(10) 34.6140(10) 13.3623(3) 22.33500(10) 13.4140(4) 54.955(3) 30.8769(2) 117.324(4)

95.187(4)

5433.3(3) 1.397 4 4.24 Cu KR 0.12, 0.09, 0.05 0.83, 1.00 132 52 431 9369 (0.099) 5455 0.061 0.15 (0.079, 0) 100

12424.5(8) 1.519 8 8.02 Cu KR 0.43, 0.16, 0.03 0.29, 0.81 135 52 838 11 025 (0.115) 8960 0.080 0.22 (0.104, 175) 200

7

9 d ,e

8

C18H22AuN2P 494.31 monoclinic P2/c (#13) 9.7136(3) 3.05710(10) 29.9700(10)

C30H22AuN2P 638.43 triclinic P1j (#2) 10.3020(8) 10.7970(8) 13.3220(10) 73.859(2) 90.363(3) 67.542(2) 68.014(2) 6622.92(9) 889.95(5) 1253.99(16) 1.338 1.845 1.691 4 2 2 3.20 8.35 5.95 Cu KR Mo KR Mo KR 0.082, 0.078, 0.034 0.17, 0.06, 0.03 0.45, 0.21, 0.10 0.82, 0.88 0.604, 1.00 0.51, 1.00 135 69 68 84 942 15 013 20 837 11 797 (0.080) 3566 (0.060) 10 166 (0.035) 9475 2800 7386 0.046 0.033 0.033 0.13 (0.091, 0) 0.045 (0.016, 0) 0.082 (0.034, 0) 100 100 296

C34.7H30.4F12N6O1.4P2Ru 944.86 triclinic P1j (#2) 11.2780(8) 13.1460(10) 13.8790(10) 69.8600(10) 88.5000(10) 84.1600(10) 1921.8(2) 1.633 2 0.589 Mo KR 0.44, 0.32, 0.12 0.485, 1.00 58 18 511 8956 (0.059) 6244 0.081 0.240 (0.116, 3.51) 170

xabs ) -0.01(4) b 0.329 PhMe solvate. c 1.54 CH2Cl2 solvate. d 2 PhMe solvate; xabs ) -0.22(10). e 1/2 H2O, 0.9 (CH3)2CO solvate.

plexes bearing alkynyl ligands with electroactive substituents, such as [(RuCl(dppe)2(C2-C6H4-p-))3N]40 and [RuCl(dppm)2(C2(2-thienyl))],41 exhibit an oxidation process assigned as being localized on the ligand moiety. The minimal difference in Ep values between the free alkynyl complexes 3 and 4 and the palladium-coordinated complex 5 appears contradictory to a bipyridyl-centered oxidation, however, whereby one would expect a greater change in oxidation potential as evinced by the significant change in energy of the corresponding bands in the UV-vis spectra (Table 2). An alternate interpretation is that this second oxidation process is indeed a bipyridyl-centered oxidation for complexes 3 and 4, with the redox process in complex 5 instead being a palladium-centered oxidation as observed in [PdCl2(bpy)] and derivatives.38 Interestingly, however, no similar additional oxidation process has been reported (40) Onitsuka, K.; Ohara, N.; Takei, F.; Takahashi, S. Dalton Trans. 2006, 3693. (41) Zhu, Y.; Millet, D. B.; Wolf, M. O.; Rettig, S. J. Organometallics 1999, 18, 1930.

Table 2. Electrochemical Data (Pt electrode, 0.1 M nBu4NPF6/ CH2Cl2, 100 mV s-1, relative to internal [FcH]/[FcH]+, E1/2 ) +560 mV) and Lowest-Energy UV-Vis Spectroscopy Absorbances of the Alkynyl Complexes λ []

E (mV) 3 4 5 a

Ox1a

Ox2b

510 600 820

1680 1530 1630

Redb

nm [104 M-1 cm-1]

-1090

386 [2.38]c 389 [2.15]c 516 [1.81]d

E1/2. b Ep. c MeCN. d CH2Cl2.

for the related complexes [CpRu(L)2(C2bpy)] (L ) PPh3, 1/2 dppf)33 or [RuCl(dppm)2(C2-2-C5H3N-5-R)] (R ) H, NO2).39 Cyclic voltammetry of the complex 5 also shows a single irreversible reduction process at -1090 mV, interpreted as a reduction of the bipyridyl moiety, a redox process presumably outside the voltammetric windows investigated for complexes 3 and 4 but anodically shifted into the observable region on coordination of the electron-withdrawing palladium center. A similar redox process at -1170 to -1340 MV has been ascribed

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Figure 4. CV traces of the ruthenium acetylide complex 4 and palladium-coordinated derivative 5 (0.1 M nBu4NPF6 in CH2Cl2, Pt disk electrode, 100 mV s-1 vs internal [FcH]/[FcH]+ couple, E1/2 ) +560 mV).

to the bipyridyl alkynyl moiety in a series of heterobimetallic ruthenium-platinum complexes derived from [(dtbpy)Pt(C2bpy)2],42 and similarly for [PdCl2(bpy)] and analogues.38 Single-Crystal X-ray Structure Determinations of Complexes 4-6. The results of the single-crystal X-ray structure determinations of 4, 5 (Figure 5), and 6 (Figure 6) are consistent in terms of stoichiometry and connectivity with the proposed formulations, variously solvated. Crystal and refinement data are collected in Table 1. The bond lengths and angles about the [RuCl(P∩P)2] cores, in 4, 5, and 6 are unremarkable and consistent with other alkynyl complexes of this type,43 and the metal-C2 parameters are also consistent with other metal-ligand systems.26 Here also the uncoordinated C2bpy units in 4 and 6 are strictly comparable to the analogous units in complexes 1 and 2. Additionally, when compared to [CpRu(dppf)(C2bpy)],33 we find that the structural parameters associated with the bipyridyl acetylide unit are also similar. Within complex 6, the two acetylides are also not significantly different. Complex 5 was produced from the addition of a PdCl2 unit to the pendant coordinating tecton in 4 and can be compared directly to that complex. While the Ru-C(1) and C(1)-C(2) distances in 5 appear significantly different from those of 6, they are consistent with the starting material, 4. In isolation it might seem that both these distances point to a delocalization of bonding and cumulene-like character in the acetylide ligand, although this is not borne out by a close examination of bonding parameters among the complexes and other ruthenium(II) acetylides. In 5 the coordination around the Pd is essentially planar, when we consider the plane defined by the coordinating nitrogen and chlorine atoms, the maximum deviating atom from that plane being N(21) (0.088(8) Å), Pd deviation (0.019(2) Å), and the angle between the rings of the bpy ligand being 6.8(2)°. Synthesis and Characterization of Some Other Alkynyl Complexes. In an effort to produce compounds capable of forming extended multimetallic complexes with interesting (42) Ziessel, R.; Seneclauze, J. B.; Ventura, B.; Barbieri, A.; Barigelletti, F. Dalton Trans. 2008, 1686. (43) Hurst, S. K.; Cifuentes, M. P.; Morrall, J. P. L.; Lucas, N. T.; Whittall, I. R.; Humphrey, M. G.; Asselberghs, I.; Persoons, A.; Samoc, M.; Luther-Davies, B.; Willis, A. C. Organometallics 2001, 20, 4664–4675.

photophysical properties, we targeted other metal complexes containing the HC2bpy tecton. During the course of our endeavors we became aware of work whose reports included full spectroscopic characterization but no single-crystal structural data of the same complexes that we had prepared, by almost identical procedures. Our procedures for the preparation of the complexes [(PEt3)Au(C2bpy)]7 (7), [(PPh3)Au(C2bpy)]7 (8), and [Ru(bpy)2(HC2bpy)](PF6)244 (9) will not be repeated here. The crystal structure of the triphenylphosphine analogue, 8, has also been obtained by us, and for the sake of completeness molecular projections have been included (Supporting Information) along with the crystal and refinement data in Table 1. Our structure is essentially identical to that reported7 and will not be discussed. Single-Crystal X-ray Structure Determinations of ([Au(PEt3)2][Au(C2bpy)2])∞ (7) and [Ru(bpy)2(HC2bpy)](PF6)2 (9). The structure of 7 provided an interesting crystallographic problem with some considerable ambiguity over which choice of space group would present the most accurate chemical picture. When projected down the crystallographic 2-axis of space group P2/c, the Au appears (incorrectly) to be fourcoordinate square planar. However, all the atoms with the exception of the Au atom have half-site occupancy. A model with these atoms at full occupancy is rendered chemically unlikely, with the neighboring ligands along the b-axis being far too close. Hence, a more sensible model would involve a two-coordinate ionic Au polymer with alternate [Au(PEt3)2]+ and [Au(C2bpy)2]- ions along the b-axis, as shown in Figure 7. We noted the pseudo-orthorhombic symmetry of the structure, but the current monoclinic cell appears to be correct. The alternate space group, Pmma, would require the C2bpy ligand to be further disordered. A search for a larger cell, possibly doubled, did not produce a significant number of extra observed data. The assignment of the N atoms on the C2bpy ligand was, rather tentatively, made on the basis of refinement and apparent location of H atoms. This type of ionic structure has been found in other coinage metal compounds, and a salient Au example is [Au(tht)I]∞ (tht ) tetrahydrothiophene),45 which exists as a one-dimensional polymer composed of alternating [AuI2]- and [Au(tht)2]+ ions. (44) Xu, H.-B.; Zhang, L.-Y.; Chen, Z.-N. Inorg. Chim. Acta 2007, 360, 163.

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Figure 5. Molecular projections and selected bond lengths (Å) and angles (deg) of (a) complex 4: Ru-C(1) 2.007(6), C(1)-C(2) 1.183(8), C(2)-C(15) 1.444(9), Ru-Cl(1) 2.4871(15), Cl(1)-Ru-C(1) 179.26(17), Ru-C(1)-C(2) 175.4(6), C(1)-C(2)-C(15) 172.3(7); (b) complex 5: Ru-C(1) 1.969(5), C(1)-C(2) 1.235(7), C(2)-C(15) 1.416(7), Ru-Cl(1) 2.4988(13), Pd-Cl(2) 2.271(2), Pd-Cl(3) 2.2835(19), Pd-N(11) 2.005(5), Pd-N(21) 2.039(6), Cl(1)-Ru-C(1) 175.69(14), Ru-C(1)-C(2) 177.9(4), C(1)-C(2)-C(15) 175.1(6), N(11)-Pd-N(21) 81.8(2), Cl(2)-Pd-Cl(3) 90.60(8).

Figure 6. Molecular projection of complex 6. Selected bond lengths (Å) and angles (deg): Ru-C(1) 2.043(5), C(1)-C(2) 1.237(7), C(2)-C(15) 1.421(7), Ru-C(3) 2.053(5), C(3)-C(4) 1.231(7), C(4)-C(41) 1.429(7), Ru-C(1)-C(2) 176.6(4), C(1)-C(2)-C(15) 172.3(5), Ru-C(3)-C(4) 176.0(4), C(3)-C(4)-C(41) 178.5(5), C(1)-Ru-C(3) 178.9(2).

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Figure 7. Molecular projection of complex 7 showing the 1-D polymer. Selected bond lengths (Å) and angles (deg): Au-C(1) 1.993(6), C(1)-C(2) 1.209(8), C(2)-C(25) 1.434(8), Au-P(1) 2.3110(14), Au-Au 3.0571(2), Au-C(1)-C(2) 176.8(5), C(1)-C(2)-C(25) 176.4(6), C(1)-Au-C(1′) 178.4(3), P(1)-Au-P(1′) 176.40(7).

Figure 8. Molecular projection of complex 9 depicting the major disordered C2bpy component.

The asymmetric unit contains two monovalent gold atoms. Both arrangements in the ions are almost linear, with the infinite Au-Au chain running along the b-axis. Least-squares planes through the coordinated atoms in the individual cations and anions are almost at right angles (88°). Similarly in 7 planes through the coordinated atoms are at ca. 86° and the aurophilic interactions are Au · · · Au 3.0571(2) Å. When compared to [Au(tht)I]∞, which has two gold atoms in the asymmetric unit and where the Au · · · Au contacts are 2.980(2) and 2.967(2) Å, the present compound has a significantly longer Au-Au contact. (45) Ahrland, S.; Nore´n, B.; Oskarsson, Å. Inorg. Chem. 1985, 24, 1330– 1333.

Another relevant example, [Ag(PMe3)2][Au(C2Ph)2], has been recently described,46 and it is interesting that the PMe3 phenylethynyl analogue of 7 is monomeric [(Me3P)(AuC2Ph)].47 The mixed coinage metal derivative has metallophilic Ag · · · Au contacts. The structure of [Ru(bpy)2(HC2bpy)](PF6)2 (9), Figure 8, was problematic, and it was found to be disordered. The major component of the structure has the acetylene group disordered on either side (C15, C15′) of the HC2bpy ligand. One PF6- anion was also found to be disordered over two sites. Additionally, there were several large peaks in the difference map, which appeared at positions corresponding to a translation of approximately (x - 0.03, y - 0.25, z) of the cation and representing the minor disordered component. Both molecules were refined, with the geometries of the minor component of the cation restrained to those of the major cation component. The geometries of the disordered PF6- groups were restrained to ideal values. Very little can be said about the minor component of the cation, as it comprises only 10% of the total and was modeled, with restraints, as being the same as the major component. While complex 9 is best compared to the reported complexes containing the [Ru(bpy)2(C2bpy)]2+ moiety from reaction of [(L)Pt(C2bpy)n] with [RuCl2(bpy)2],42,44 there is no structural information relevant to the complex of interest. Thus when compared to other [Ru(bpy)2(5-R-bpy)]2+ cations structurally characterized that are substituted at the 5-position on one of the bipyridyl ligands, e.g., [Ru(bpy)2(5-pyrenebpy)]2+,48 there is very little that is remarkable about the geometry of either complex. In fact, given the disorder in (46) Schuster, O.; Monkowius, U.; Schmidbaur, H.; Ray, R. S.; Kruger, S.; Rosch, N. Organometallics 2006, 25, 1004–1011. (47) Schuster, O.; Liau, R.-Y.; Schier, A.; Schmidbaur, H. Inorg. Chim. Acta 2005, 358, 1429–1441. (48) Beinhoff, M.; Weigel, W.; Jurczok, M.; Rettig, W.; Modrakowski, C.; Bru¨dgam, I.; Hartl, H.; Schlu¨ter, A. D. Eur. J. Org. Chem. 2001, 2001, 3819–3829.

Coordinating Tectons

the system very few conclusions can be drawn from the interatomic parameters of 9.

Summary and Conclusions We have shown that it is possible to synthesize bipyridylsubstituted acetylides using 5-ethynyl-2,2′-bipyridine. We have also found that, due to the basicity of the bipyridine moiety, the preparation of σ-alkynyls using standard vinylidene methodology is fraught with problems leading to mixtures of compounds in the case of bis-diphosphine complexes. However, in the case of the [CpRu(CO)2] and [PR3Au] fragments the formation of alkynyls is trivial. We have also prepared a heterometallic Ru-Pd complex, thus demonstrating the potential of these complexes as tectons for the preparation of extended architectures. The effect of the Pd atom on the physical properties of the alkynyl complex has been investigated using cyclic voltammetry and spectroscopic techniques.

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We are currently investigating the general utility of the organometallic coordination polymer approach to molecular wires.

Acknowledgment. We thank the University of Western Australia for partly funding this project. P.A.S. was the holder of an Australian Postgraduate Award. G.I.J. was a recipient of the Raoul Robellaz Kahan Scholarship in Chemistry. Supporting Information Available: 1H,13C-HSQC and 1H,13CHMBC NMR spectra of 2 and molecular projection and unit-cell diagram of 8. This material is available free of charge via the Internet at http://pubs.acs.org. CCDC 718049-718051, 718730718733, 723100 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif. OM800992P